Presently, studies are underway to use RACH (Random Access Channel) for initial access from a radio communication mobile station apparatus (hereinafter simply “mobile station”) to a radio communication base station apparatus (hereinafter simply “base station”), in 3GPP RAN LTE (long term evolution) (e.g. see Non-Patent Document 1). The RACH is utilized in initial access, for example, upon making an association request and a resource request to the base station, and acquiring uplink transmission timing synchronization.
A mobile station transmitting a RACH signal selects one of a plurality of unique signatures in the RACH and transmits the selected signature to the base station to distinguish itself from other mobile stations transmitting RACH signals.
Moreover, in the RACH, taking into account that a plurality of signatures are transmitted from a plurality of mobile stations at the same time, studies are underway to use code sequences of low cross-correlation and high autocorrelation as signatures so as to demultiplex and detect those signatures in the base station. As a code sequence having such characteristics, the CAZAC (Constant Amplitude Zero Auto-Correlation) sequence is known, which is one of GCL (Generalized Chirp-Like) sequences (e.g. see Non-Patent Document 2).
As shown in FIGS. 1A to 1C, RACH frame configurations where preamble parts and message parts are time-multiplexed, are proposed (e.g. see Non-Patent Document 1). The transmission power of the preamble part and the message part can be determined by open-loop transmission power control. Open-loop transmission power means to determine uplink transmission power using downlink common channel received levels. The base station maintains constant received power between the mobile stations of different propagation losses, so that the rate of detection of the RACHs of a plurality of mobile stations is improved.
Moreover, the rate of detection of the RACH is improved through transmission in different access slot lengths according to the size of propagation loss.
Non-patent Document 1: 3GPP TSG-RAN WG1 LTE Ad Hoc Meeting, R1-060047, NTT DoCoMo, NEC, Sharp, “Random Access Transmission in E-UTRA Uplink,” Helsinki, Finland, 23-25 Jan. 2006
Non-patent Document 2: 3GPP TSG-RAN WG1 LTE Ad Hoc Meeting, R1-060046, NTT DoCoMo, NEC, Sharp, “Orthogonal Pilot Channel Structure in E-UTRA Uplink,” Helsinki, Finland, 23-25 Jan. 2006